This sentence is actually **ambiguous** — it's not possible to definitively determine who "she" refers to based on the sentence alone.

- **"She"** could refer to **the nurse** (the doctor called to find out where the nurse was).
- **"She"** could also refer to **the doctor** (the doctor was running late and called the nurse to let her know).

The sentence is a classic example used in linguistics and AI research (known as a **Winograd schema**) to illustrate how pronoun resolution often depends on context and common-sense reasoning rather than grammar alone.

That said, many people instinctively read "she" as referring to **the nurse**, since "phoned someone *because she was late*" most naturally suggests the late person is the one being called. But without more context, both interpretations are valid.
